(function flexible(window, document) {
  var docEl = document.documentElement;
  var dpr = window.devicePixelRatio || 1;

  // adjust body font size
  function setBodyFontSize() {
      if (document.body) {
          document.body.style.fontSize = 12 * dpr + "px";
      } else {
          document.addEventListener("DOMContentLoaded", setBodyFontSize);
      }
  }
  setBodyFontSize();

  // set 1rem = viewWidth / 10
  function setRemUnit() {
      // 这里默认是10等份，手动改为24，此时1rem=1920/24px即80px。（设计稿是1920px的）
      var rem = docEl.clientWidth / 24;
      docEl.style.fontSize = rem + "px";
  }

  setRemUnit();

  // reset rem unit on page resize
  window.addEventListener("resize", setRemUnit);
  window.addEventListener("pageshow", function (e) {
      if (e.persisted) {
          setRemUnit();
      }
  });

  // detect 0.5px supports
  if (dpr >= 2) {
      var fakeBody = document.createElement("body");
      var testElement = document.createElement("div");
      testElement.style.border = ".5px solid transparent";
      fakeBody.appendChild(testElement);
      docEl.appendChild(fakeBody);
      if (testElement.offsetHeight === 1) {
          docEl.classList.add("hairlines");
      }
      docEl.removeChild(fakeBody);
  }
})(window, document);